Purified toxin fractions from the scorpion, centruroides sculpturatus Ewing will be studied for their actions on the isolated nerve and neuromuscular junction using both mammalian (guinea pig - rat) and non-mammalian (frog) vertebrate tissues. Techniques will be used to measure a) intracellular postsynaptic potentials and b) extracellular presynaptic potentials, as well as c) twitch tension development. In addition, d) effects of the toxin fractions will be examined on the axon membrane (frog node of Ranvier preparation) by electrophysiologic methods. Experiments will be designed to relate toxic activities to effects on ionic constituents of the membrane (Na ion, K ion, Ca ions) and to acetylcholine content and release. e) Possible structural changes in the membrane systems will be examined by light and electron microscopy. The following controls with frog muscle are appropriate and will be studied as a corollary to this proposal: 1) Investigation of the release of Ca ions from intracellular stores by scorpion venom using the histochemical technique of calcium binding by alizarin red sulfonate; 2) Determination of the presence or absence of so called sarcomeric oscillations under the influence of scorpion venom; 3) Analysis of spontaneous venom-induced muscle fiber activity will be investigated by means of denervated frog muscle to ascertain the role (or lack of it) of post-synaptic processes.